Such a wet clutch friction plate is already known, as disclosed in, for example, Japanese Patent Application Laid-open No. 2001-221252.
In such a wet clutch friction plate it is necessary, for example, to improve frictional properties in order to suppress the occurrence of abnormal noise or vibration due to stick-slip by stabilizing frictional properties when connection of the clutch is in transition even under conditions in which there is a small amount of oil (first problem), and it is also necessary to reduce the phenomenon of drag due to oil viscosity resistance when the clutch is disengaged (second problem).
However, conventionally, countermeasures are taken against the first problem by reducing the oil discharge properties by narrowing the width of the oil channels on the surface of the friction material, whereas countermeasures are taken against the second problem by enhancing the oil discharge properties by widening the width of the oil channels on the surface of the friction material, which is the opposite of the above-mentioned countermeasures; as a consequence, it is difficult to solve the two problems simultaneously and, in reality, solution of one of the first and second problems is sacrificed in accordance with the intended application or the specification of the wet clutch.